Ultrafast removal of organics via peroxymonosulfate activation over Co2P/TD hollow spheres derived from ZIF-67.

Co2P/tetrasodium diphosphate (TD) derived from ZIF-67/sodium phytate was newly developed and synthesized, and exhibited excellent degradation ability toward various refractory organics via peroxymonosulfate activation. A corresponding reaction mechanism was proposed. In addition, a continuous-flow operation of phenol degradation was realized.

Fe-Cu bimetal metal-organic framework for efficient decontamination via Fenton-like process: Synthesis, performance and mechanism.

Constructing Fe-Cu bimetal catalysts is an efficient strategy to promote Fe(III)/Fe(II) cycle, whereas there is still a long way to go before fully understanding the role of the Cu in the catalysts. Herein, a new Fe-MOF namely BUC-96(Fe) was fabricated from FeSO4·7H2O, 4,4'-bipyridine (bpy) and 2,5-dihydroxyterephthalic acid (H4dhtp) by both hydrothermal reaction and microwave-assisted method. Also, bimetal BUC-96(FeCu-x) were obtained when the CuSO4 was added into the system identical to the synthesis process of BUC-96(Fe). Series BUC-96 MOFs showed good organics elimination performance via Fenton-like process, where 88.1% (k = 0.0672 min-1) of chloroquine phosphate (CQ, 20 mg/L) was decomposed over pristine BUC-96(Fe) within 30 min. Interestingly, nearly 100% CQ was degraded over BUC-96(FeCu-5) as catalyst under the identical conditions within 5 min, whose reaction rate (1.3527 min-1) was 20.1-fold higher than that of BUC-96. Additionally, BUC-96(FeCu-5) exhibited excellent Fenton-like oxidation degradation performance for 10 selected emerging organic pollutants. The reaction mechanism was studied in detail by experiments, and density functional theory (DFT) calculation. The results revealed that the introduced Cu not only accelerated Fe(III)/Fe(II) cycles, hydroxyl radical (·OH) generation, electron transfer, but also lowered H2O2 dissociated energy barrier. This work advanced the bimetal MOFs construction and application in wastewater treatment via Fenton-like process.

Enhanced photo-Fenton activity and stability for sulfamethoxazole degradation by FeS2@TiO2 heterojunction derived from MIL-125.

FT-x composites with core-shell structure (FT = FeS2@TiO2, x represents the mass ratio of the used FeCl3·6H2O to MIL-125) were fabricated by a hydrothermal method using MIL-125(Ti) as a self-sacrificing template. Both the photo-Fenton activity and stability of the FT-1 were improved greatly in comparison with its counterparts due to the unique core-shell structure and synergistic effect between FeS2 and TiO2. Especially, the Fe leaching concentration of FT-1 was approximately 1/10 of the individual FeS2, benefiting from the protection effect of TiO2 shell. Under dark condition, the formed FeOOH occupied active sites and inhibited iron cycle as well as H2O2 decomposition, leading to the inactivation of FT-1. UV light irradiation not only boosted the catalytic activity but also prevented the FT-1 from reactivity decline owning to the regeneration of Fe2+ by photogenerated electrons and continuous generation of ·OH. Experimental and DFT calculation results indicated that a type-II heterojunction was formed, in which photogenerated electrons were transferred from FeS2 core to TiO2 shell, accelerating charge separation and further boosting sulfamethoxazole (SMX) degradation. FT-1 displayed outstanding photo-Fenton activity in wide pH ranged from 2 to 6 and good anti-interfering ability toward impurities in water matrix. Besides, the reusability of FT-1 was good, in which 90% SMX degradation was maintained even after 5 runs. Noteworthy, the photo-Fenton activity was recovered via a revulcanization process, in which FeOOH was completely transformed into FeS2. This founding provided insights for the design and construction of heterojunction with both excellent photo-Fenton activity and stability.

High-efficient peroxymonosulfate activation for rapid atrazine degradation by FeSx@MoS2 derived from MIL-88A(Fe).

FeSx@MoS2-x (FM-x, x implied real Mo/Fe content ratios) in which FeSx derived from MIL-88A deposited on the surface of MoS2 with a tight heterogeneous interface were synthesized for peroxymonosulfate (PMS) activation to degrade atrazine (ATZ). The catalytic performance of FM-0.96 was greatly improved due to the rapid regeneration of Fe2+ resulting from the interfacial interaction. FM-0.96 could completely degrade 10.0 mg/L ATZ within 1.0 min, and the toxicities for most of its intermediates were greatly reduced. The k value of FM-0.96 was 320 and 40 times higher than that of the MoS2 and FeSx, respectively. The SO4·-, ·OH and 1O2 were mainly responsible for ATZ degradation in FM-0.96/PMS system, and the conversion pathway of 1O2 was analyzed. Furthermore, the long-term continuous operation for ATZ degradation was achieved using a fixed membrane reactor. This work provides deep insights into metal sulfide composites derived from metal-organic frameworks for removing pollutants by activating PMS.

Enhanced catalytic sulfamethoxazole degradation via peroxymonosulfate activation over amorphous CoSx@SiO2 nanocages derived from ZIF-67.

In this work, the amorphous CoSx@SiO2 nanocages were hydrothermally synthesized by sulfurizing ZIF-67@SiO2 in the presence of thioacetamide (TAA). The catalytic performances of CoSx@SiO2 nanocages as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the sulfamethoxazole (SMX) degradation were systematically investigated. 100% SMX was degraded within 6 min in CoSx@SiO2/PMS system, indicating that the amorphous CoSx@SiO2 nanocages exhibited outstanding sulfate radical-advanced oxidation process (SR-AOP) activity toward SMX degradation due to the regeneration of Co2+ by surficial sulfur species like S2-/S22-. The effects of PMS dosages, initial pH, SMX concentrations and co-existing ions on SMX degradation efficiency were explored in detail. The SMX removal efficiency was obviously improved in the simulated wastewater containing chloride ions (Cl-) and low-concentration bicarbonate ions (HCO3-). The residual PMS and the generated sulfate radical (SO4·-) were determined quantitatively in CoSx@SiO2/PMS system. A possible mechanism in CoSx@SiO2/PMS system was proposed based on the results of quenching experiments, X-ray photoelectron spectroscopy (XPS) analysis, electrochemical tests, and electron spin resonance (ESR). The CoSx@SiO2 exhibited good stability and reusability, in which 100% SMX removal was achieved even after five consecutive cycles. This work provided a strategy for regulating the stability of cobalt-based catalyst for efficient pollutant degradation by PMS activation.

Enhanced catalytic peroxymonosulfate activation for sulfonamide antibiotics degradation over the supported CoSx-CuSx derived from ZIF-L(Co) immobilized on copper foam.

The CoSx-CuSx was firmly immobilized on copper foam (CF) substrate to fabricate supported CoSx-CuSx/CF using ZIF-L(Co)/CF as a self-sacrificing template, in which CF substrate played an important role in improving the adhesion between CF and target catalyst as well as the interfacial interaction between CoSx and CuSx. The CoSx-CuSx/CF performed well in catalytic peroxymonosulfate (PMS) activation, which can accomplish 97.0% sulfamethoxazole (SMX) degradation within 10 min due to the special structure and Co2+ regeneration promoted by S2- and Cu+. The influences of pH, PMS dosage, catalyst dosage, co-existing anions and natural organic matter (NOM) on SMX removal were studied in detail. CoSx-CuSx/CF presented excellent catalytic activity and reusability, which might be fascinating candidate for real wastewater treatment. The possible pathway of SMX degradation was proposed, and the toxicity of the intermediates during the degradation process were evaluated. It is noteworthy that long-term continuous degradation of sulfonamide antibiotics was achieved using a self-developed continuous-flow fixed-bed reactor. This work demonstrated that CF as a substrate to fabricate supported catalysts derived from MOF had great potential in actual wastewater remediation.

Heterogeneous photo-Fenton degradation toward sulfonamide matrix over magnetic Fe3S4 derived from MIL-100(Fe).

Magnetic Fe3S4 was facilely derived from MIL-100(Fe) as the precursor and thioacetamide (TAA) as the sulfur source under hydrothermal condition. The as-prepared Fe3S4 was adopted as catalyst to promote the photo-Fenton process, in which sulfamethoxazole (SMX) was used as representative pollutant sample to test the oxidative degradation performance of Fe3S4. The results showed that Fe3S4 exhibited excellent photo-Fenton-like oxidation decomposition performances toward sulfamethoxazole (SMX) under both UV and visible light. A possible degradation mechanism over Fe3S4 in the photo-Fenton reaction is put forward based on quenching experiments and electron spin resonance (ESR). About 41% total organic carbon (TOC) removal efficiency of sulfamethoxazole (SMX) over the as-prepared Fe3S4 can be accomplished within 40 min. As well, different sulfonamide antibiotics (SAs) like sulfamethoxazole (SMX), sulfisoxazole (SIM) and sulfadiazine (SDZ) were selected to further investigate the oxidative degradation activity of Fe3S4 in this photo-Fenton-like reaction system, in which the possible degradation pathways of SMX, SIM and SDZ were put forward based on UHPLC-MS analysis. This work provided a new strategy to prepare magnetic Fe3S4 as catalyst for advanced oxidation process, which can be easily separated from the treated water samples to accomplish facile recovery and recyclability.

Construction of direct Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts for enhanced degradation of ciprofloxacin: Mechanism insight, pathway analysis and toxicity evaluation.

Direct Z-scheme Bi5O7I/UiO-66-NH2 (denoted as BU-x) heterojunction photocatalysts were successfully constructed through ball-milling method. Photocatalytic activities of the as-prepared BU-x samples were determined by using a typical fluoroquinolone antibiotic, ciprofloxacin (CIP). All BU-x heterojunctions exhibited better CIP removal performances than that of pristine Bi5O7I and UiO-66-NH2 upon exposure to white light irradiation. In comparison, the heterojunction with UiO-66-NH2 content of 50 wt% (BU-5) showed excellent structural stability and the optimal adsorption-photodegradation efficiency for the CIP removal. The removal efficiency of CIP (10 mg/L) over BU-5 (0.75 g/L) achieved 96.1% within 120 min illumination. Meanwhile, the effect of photocatalyst dosage, pH and inorganic anions were systemically explored. Reactive species trapping experiments, electron spin resonance (ESR) signals, Mott-Schottky measurements and density functional theory (DFT) simulation revealed that the photo-generated holes (h+), hydroxyl radical (·OH) and superoxide radical (·O2-) played crucial roles in CIP degradation. This result can be ascribed to that the unique Z-scheme charge transfer configuration retained the excellent redox capacities of Bi5O7I and UiO-66-NH2. Meanwhile, the CIP degradation pathways and the toxicity of various intermediates were subsequently analyzed. This work provided a feasible idea for removing antibiotics by bismuth-rich bismuth oxyhalide/MOF-based heterostructured photocatalysts.

Bisphenol A cleanup over MIL-100(Fe)/CoS composites: Pivotal role of Fe-S bond in regenerating Fe2+ ions for boosted degradation performance.

Series of MIL-100(Fe)/CoS composites (MxCy) were facilely fabricated using ball-milling method. The optimum M50C50 exhibited extremely higher Fenton-like catalytic degradation activity toward bisphenol A (BPA) than the pristine MIL-100(Fe) and CoS. The significant improvement of BPA degradation was attributed to the synergetic effect between MIL-100(Fe) and CoS with the synergistic factor being 95.7%, in which the Fe-S bonds formed at the interface of the two components facilitate the Fe3+/Fe2+ cycle by improving the electron mobility both from Co to Fe and from S to Fe. Furthermore, the influence factors like co-existing inorganic ions and pH values on the catalysis activity of M50C50 were explored. The possible reaction mechanism was proposed and confirmed by both active species capture tests and electron spin resonance (ESR) determinations. It was found that M50C50 demonstrated good reusability and water stability, in which the morphology and structure were not changed obviously after five runs' operation. To our best knowledge, it is the first work concerning the interfacial interaction of Fe-MOF/MSx to promote Fe3+/Fe2+ cycle in Fe-MOFs for the purpose of organic pollutants degradation in the Fenton-like AOPs system.

Porous Cd0.5Zn0.5S nanocages derived from ZIF-8: boosted photocatalytic performances under LED-visible light.

A facile strategy was adopted to prepare porous Cd0.5Zn0.5S (CZS-X) nanocages by sulfurizing the rhombic dodecahedral ZIF-8 as precursor with thioacetamide (TAA) at different durations (0, 1, 3, 5 h), in which the fabrication mechanism of the porous CZS-X nanocages was clarified. The photocatalytic activities of CZS-X for Cr(VI) elimination and organic pollutant decomposition were assessed. The results revealed that CZS-3 exhibited optimal photocatalytic activity under visible light along with satisfied recyclability and stability after several runs' operation. As well, the CZS-3's photocatalytic cleanup abilities toward both Cr(VI) and organic pollutants were explored in different actual water bodies to clarify the influence of different foreign ions. Finally, the intrinsic photocatalysis mechanism of CZS-X was verified.

S-TiO2/UiO-66-NH2 composite for boosted photocatalytic Cr(VI) reduction and bisphenol A degradation under LED visible light.

Series sulfur-doped TiO2/amine-functionalized zirconium metal organic frameworks (S-TiO2/UiO-66-NH2) composites (U1Tx) were facilely fabricated from the as-prepared S-TiO2 and UiO-66-NH2 via ball-milling method. The photocatalytic activities of U1Tx toward Cr(VI) reduction and bisphenol A (BPA) degradation were tested under low-power LED visible light. The results demonstrated that U1T3 exhibited better photocatalytic performances than the pristine S-TiO2 and UiO-66-NH2 due to the improved separation and migration of electrons and holes. Furthermore, the influence factors like pH values and foreign ions on the photocatalytic performances of U1Tx were also investigated. The Box-Behnken design methodology was utilized to further clarify that the inorganic foreign anions and dissolved organic matters could exert significant effects on photocatalytic Cr(VI) reduction performance. As well, the possible pathway of BPA degradation was depicted. After four runs of Cr(VI) removal, it was found that U1T3 exhibited preferable reusability and water stability. The probable reaction mechanism was proposed and verified by active species capture experiments, electron spin resonance determination and electrochemical analyses.

Superior removal of inorganic and organic arsenic pollutants from water with MIL-88A(Fe) decorated on cotton fibers.

Arsenic contamination has attracted worldwide concerns, owing to its toxicity and severe threat to human and environment. It is urgent to develop efficient adsorbents to remove arsenic pollutants. Within this paper, both pristine MIL-88A(Fe) and MIL-88A(Fe) decorated on cotton fibers were successfully fabricated using an eco-friendly method. The pristine MIL-88A(Fe) displayed outstanding adsorption performances towards four selected arsenic pollutants, in which the adsorption capacities toward As(III), As(V), ROX and ASA were 126.5, 164.0, 261.4 and 427.5 mg g-1, respectively. Additionally, MIL-88A(Fe) exhibited excellent removal efficiencies in a wide pH range and with the presence of different co-existing ions. It was proposed that the coordinative interactions of As-O-Fe between arsenic pollutants and MIL-88A(Fe) contributed to the superior adsorption performances. Furthermore, two MIL-88A(Fe)/cotton fibers composites were synthesized by both post synthesis (MC-1) and in-situ synthesis (MC-2), which demonstrated identically outstanding adsorption activities toward four selected arsenic pollutants. MC-1 and MC-2 enhanced the stability and reusability of MIL-88A(Fe), which was challenging issues of pristine MIL-88A(Fe) powder. Additionally, the fixed-bed column packed by MC-1 or MC-2 can continuously eliminate arsenic pollutants from the water flow. This work provided a new possibility of metal-organic frameworks to accomplish potentially large-scale application to purify the arsenic-contaminated water.

Porous tube-like ZnS derived from rod-like ZIF-L for photocatalytic Cr(VI) reduction and organic pollutants degradation.

A facile method was developed to fabricate porous tube-like ZnS by sulfurizing rod-like ZIF-L with thioacetamide (TAA) at different durations and the formation mechanism of the porous tube-like ZnS was discussed in detail. The series of sulfide products (ZS-X) were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (SSNMR), transmission electron microscopy (TEM), UV-visible diffuse-reflectance spectroscopy (UV-vis DRS). The photocatalytic performances of ZS-X toward Cr(VI) reduction and organic pollutant degradation were explored. It was discovered that ZS-3 (porous tube-like ZnS) exhibited excellent activities under UV light and displayed good reusability and stability after several experimental cycles. In addition, Cr(VI) reduction and organic pollutant degradation were investigated under different pH values and existence of different foreign ions. The photocatalytic activities of ZS-3 were tested toward the matrix of Cr(VI) and reactive red X-3B. The mechanism was proposed and verified by both electrochemical analysis and electron spin resonance (ESR) measurement.

Polyaniline modified MIL-100(Fe) for enhanced photocatalytic Cr(VI) reduction and tetracycline degradation under white light.

The Z-scheme MIL-100(Fe)/PANI composite photocatalysts were facilely prepared from MIL-100(Fe) and polyaniline (PANI) by ball-milling, and were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), UV-visible diffuse-reflectance spectrometry (UV-vis DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence emission spectrometry (PL). The photocatalytic activities of MIL-100(Fe)/PANI composites were investigated via tetracycline degradation and hexavalent chromium reduction in aqueous solution under the irradiation of white light. The results revealed that the MIL-100(Fe)/PANI composite photocatalysts exhibited outstanding photocatalytic activities toward Cr(VI) reduction and tetracycline decomposition. The effects of pH and coexisting ions on the photocatalytic Cr(VI) reduction were investigated. As well, the primary active species were identified via electron spin resonance (ESR) determination. A possible Z-scheme photocatalyst mechanism was proposed and verified. Finally, MIL-100(Fe)/PANI composites demonstrated good reusability and stability in water solution, implying potentially practical applications for real wastewater treatment.

Simultaneous Cr(VI) reduction and Cr(III) removal of bifunctional MOF/Titanate nanotube composites.

In this study, a series of BUC-21/titanate nanotube (BT-X) composites were facilely fabricated via ball-milling of 2-dimensional (2D) metal-organic framework (MOF) BUC-21 and titanate nanotubes (TNTs). The BT-X composites were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-visible diffuse-reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectrometer (XPS) and high resolution transmission electron microscopy (HRTEM). Both the photocatalytic reduction from Cr(VI) to Cr(III) and adsorptive removal of formed Cr(III) of BT-X composites were systematically investigated under different conditions including pH values and co-existing inorganic ions. It was found that BUC-21 (100 mg)/TNTs (100 mg) (BT-1) composites demonstrate remarkable ability of photocatalytic Cr(VI) reduction and adsorptive Cr(III) removal, as well as good reusability and stability. It is believed that the introduction of TNTs could capture the formed Cr(III) from the surface of BUC-21, which provided more active sites exposed to enhance the Cr(VI) reduction.

The selectively fluorescent sensing detection and adsorptive removal of Pb2+ with a stable [δ-Mo8O26]-based hybrid.

A polyoxomolybdate based hybrid, [δ-Mo8O26](L)2·2H2O (BUC-77), was synthesized via hydrothermal method, which exhibited selectively fluorescent detection and efficient adsorptive removal toward Pb2+ in aqueous environment. A good linearity was observed between the fluorescence quenching percentage of BUC-77 and the Pb2+ concentration, along with the detection limit being 6.91 ppb. BUC-77 was stable in common solvents and wide pH range, which could be regenerated by being washed with dilute inorganic acids like HNO3 after adsorption of Pb2+. The results revealed that BUC-77 could be potentially used to achieve both detection and removal of Pb2+ in wastewater.

Enhanced acetone sensing performance of Au nanoparticle modified porous tube-like ZnO derived from rod-like ZIF-L.

Metal oxide semiconductors with a porous hollow structure have received great attention in many fields. In this work, a facile preparation method of porous tube-like ZnO (PT-ZnO) was developed by annealing rod-like ZIF-L at high temperature, and the formation mechanism of the tube-like structure was discussed in detail. The corresponding gas sensing performances were determined adopting acetone as the target gas. Gas-sensing test results show that PT-ZnO has better acetone sensing performance than that of porous plate-like ZnO (PP-ZnO) derived from leaf-like ZIF-L, resulting from the unique tube-like structure and larger amount of adsorbed oxygen. It is found that the introduction of Au nanoparticles greatly improves the acetone sensing performance, which can be attributed to the activation of acetone by Au and the increased amount of adsorbed oxygen. Au/PT-ZnO has the largest amount of adsorbed oxygen which even becomes the dominant oxygen species on the surface of PT-ZnO, resulting in the best acetone-sensing performance.

Selective adsorption activities toward organic dyes and antibacterial performance of silver-based coordination polymers.

Two silver-based coordination polymers, [Ag2(bpy)2(cbda)] (BUC-51) and [Ag3(bpy)3(cpda)]·(NO3)·9H2O (BUC-52), have been successfully prepared by slow evaporation at room temperature. These coordination polymers exhibited good adsorptive performances toward series organic dyes with sulfonic groups, which could be ascribed to the AgcdotsO interaction between the silver(I) atoms in CPs and the oxygen atoms from sulfonic groups attached to organic dyes. Both BUC-51 and BUC-52 favoured slow release of Ag+ ions resulting into outstanding long-term antibacterial abilities toward Gram-negative bacteria, Escherichia coli (E. coli), which was tested by a minimal inhibition concentration (MIC) benchmark and an inhibition zone testing method. Both scanning electron microscope (SEM) and transmission electron microscope (TEM) images demonstrated that these two Ag-based coordination polymers could destroy the bacterial membrane and further cause death. Additionally, the excellent stability in common solvents and good optical stability under UV-visible light facilitated their adsorptive and antibacterial applications.

High-performance adsorption and separation of anionic dyes in water using a chemically stable graphene-like metal-organic framework.

A highly stable graphene-like metal-organic framework (BUC-17) was prepared and used as an adsorbent to carry out the adsorption of anionic dyes from simulated wastewater, which exhibited excellent adsorption performance, particularly towards Congo red (CR) up to 4923.7 mg g-1 at room temperature. It was used to fix a SPE column to conduct rapid separation of anionic dyes from an organic dye matrix. A related mechanism was also proposed.

Strong metal-support interaction in novel core-shell Au-CeO2 nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation.

Yolk-shell Au/CeO2 (Y-Au/CeO2) and encapsulated Au/CeO2 (E-Au/CeO2) nanocatalysts were prepared by using silica templates. A strong metal-support interaction (SMSI) in the Au/CeO2 nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation were studied. E-Au/CeO2 pretreated in O2 had the best performance, followed by Y-Au/CeO2 pretreated in O2, Y-Au/CeO2 pretreated in H2, and E-Au/CeO2 pretreated in H2. The reasons for the different activities were discussed. There were two kinds of strong metal-support interactions (SMSI) between Au and CeO2 termed as R-SMSI (pretreated in reductive atmosphere) and O-SMSI (pretreated in oxidation atmosphere). Because of the smaller size of the Au and the larger contact area, both the R-SMSI and O-SMSI of E-Au/CeO2 were larger than those of Y-Au/CeO2. The O-SMSI was accompanied by the formation of cationic Au species that were beneficial to the enhancing of activity. As expected, the activity of E-Au/CeO2 pretreated in O2 with a Au size less than 5 nm was higher than that of Y-Au/CeO2 pretreated in O2 with 25 nm Au. However, it is surprisingly found that the activity of Y-Au/CeO2 pretreated in H2 with 25 nm Au was higher than that of E-Au/CeO2 pretreated in H2 with a Au size less than 5 nm. R-SMSI resulted in the formation of a AuCe alloy that had a negative effect on the activity. Compared with E-Au/CeO2 pretreated in H2, Y-Au/CeO2 pretreated in H2 exhibited a smaller relative content of the AuCe alloy, leading to a better activity of Y-Au/CeO2 pretreated in H2.